1. Field of the Invention
The present invention relates to an image forming apparatus and a process cartridge used for the image forming apparatus.
Herein, the image forming apparatus is an apparatus that forms an image on a recording medium by using an electrophotographic method.
In addition, examples of the image forming apparatus include copying machines, printers (e.g., laser beam printers, LED printers), facsimile machines, and word processors that use the electrophotographic method.
2. Description of the Related Art
In an electrophotographic image forming apparatus (hereinbelow, also simply referred to as an image forming apparatus), an electrophotographic photosensitive member (hereinbelow, also simply referred to as a photosensitive member) as an image bearing member is uniformly charged. Then, the charged photosensitive member is selectively exposed to light according to image information, and an electrostatic image (electrostatic latent image) is formed on the photosensitive member. The electrostatic image is developed (visualized) as a toner image (developer image) with developer. Then, the toner image is transferred to a recording medium. Thereafter, the toner image is fixed and recorded to the recording medium by adding heat and pressure to the recording medium to which the toner image is transferred.
In the image forming apparatus, in order to form an image, the photosensitive member of a process cartridge mounted on the image forming apparatus main body and a process unit (process member) acting on the photosensitive member need to be rotated. The photosensitive member and process unit are subjected to electrostatic or physical actions respectively by elements such as other process units. Therefore, a specific torque is needed to rotate the photosensitive member or the process unit.
The torque required for the rotation may vary due to the influence of the rotation period of the photosensitive member or the process unit. However, during image formation, if fluctuation of torque occurs, the rotational circumferential speed of the photosensitive member or the developer bearing member serving as the process unit may vary to cause image defect such as density unevenness or pitch unevenness.
Therefore, Japanese Patent Application Laid-open No. 05-080651 discusses a technique in which a drive path of an agitation member, which is susceptible to a load fluctuation caused by agglutination of developer, is provided in a different route from the drive path of the photosensitive member or the developer bearing member.
However, with the above-described conventional configuration, if the developer bearing member and the agitation member are driven at a same time during image formation, a common drive source mounted in the image forming apparatus main body needs to provide a drive torque of the agitation member in addition to a drive torque of the developer bearing member.
Therefore, in order to reduce the influence of the variation of the rotation period of the developing unit as described above, a power source that can supply larger power is required, resulting in increase in cost or power consumption.
This applies to a case where drive sources are provided independently for driving the developer bearing member and the agitation member.
In addition, not limited to the developer bearing member, the same problem may occur when the photosensitive member (image bearing member) and the agitation member are driven at a same time.